The outer capsid of group A rotaviruses is comprised of two proteins: VP4 (encoded by genome segment 4) and VP7 (encoded by genome segment 7,8 or 9 depending on the strain), both of which are distinct neutralization antigens. Because neutralizing antibodies appear to play an important role in protection against many viral diseases, the two outer capsid rotavirus antigens (VP4 and VP7) that induce neutralizing antibodies have played a central role in the research and development of a rotavirus vaccine. Classification of rotaviruses into serotypes according to VP7 specificity by neutralization has progressed smoothly by adopting principles previously applied to other viruses. The cornerstone of this system is that a strain is considered to be a distinct serotype when a reciprocal >20-fold difference in neutralizing antibody titer is observed between that strain and established serotypes. Based on this criterion, fourteen VP7 serotypes (G serotype) have been defined. However, there is considerable confusion regarding the classification of strains according to VP4 specificity because of the lack of specific antisera that recognize VP4 neutralization specificity. As a result, a few strains have been classified by neutralization but most have been assigned numbers according to VP4 genetic relationships on the basis of nucleic acid hybridization and sequence analysis of the VP4 gene. However, a genotype established by nonserological methods is not always identical to a serotype defined by serological methods. An analysis of the neutralization specificity on both VP7 and VP4 is needed for a better understanding of rotavirus epidemiology and for formulation of an effective strategy for control of rotavirus disease by immunization. Objectives in this project are three-fold: (i) to cultivate directly in cell cultures a variety of human and animal rotavirus strains derived from diverse geographical areas and populations; (ii) to define serotypic diversity and similarity among these viruses based on their VP4 and VP7 specificities; and (iii) to select and develop potential rotavirus vaccine candidates (as described in project "Genetic studies of Rotavirus Pathogenesis"). The educidation of the neutralization specificities of rotavirus is important in order to achieve a more comprehensive understanding of rotavirus epidemiology and for formulation of an effective strategy for vaccination.